1. Field of the Invention
The present invention relates to a control apparatus and method for an engine-motor hybrid vehicle, and more particularly to a control apparatus and method which compensates for a lessening of an engine by learning.
2. Description of Related Art
An engine-motor hybrid vehicle, such as disclosed in EP 0800951A1 (JP-A-9-266601), has an internal combustion engine, a power transmission device including a rotary electric machine (electric motor) which converts a part of an engine power or the entirety thereof into an electric power to generate at least one part of the driving power of the vehicle, and an electricity storage device (storage battery) for supplying the electric power to the rotary electric machine and receiving it therefrom. The power transmission device is a two-motor type, which has a first rotary electric machine connected with an output shaft of the engine and determines the number of rotations of the engine, and a second rotary electric machine connected with an output shaft of a vehicle body and determines the driving force of the vehicle.
In this type of hybrid vehicle, it is necessary to control the engine by an electronic control unit the rotary electric machine, and the electricity storage device. Specifically, the electronic control unit calculates a vehicle driving torque demand value corresponding to a depression stroke of an accelerator pedal. Based on the number of rotations of the output shaft of the vehicle, the control unit also calculates a vehicle driving power demand value to be outputted to the drive shaft. The control apparatus also calculates an engine torque demand value corresponding to the vehicle driving power demand value and calculates an engine speed demand value corresponding thereto. Then, the control unit calculates an engine power demand value, based on the determined engine torque demand value and the determined engine speed demand value. To obtain a high degree of engine efficiency, the control unit determines an engine operation point on an engine performance characteristics curve which displays the engine power demand.
To operate the engine in a steady state at the engine operation point, a torque control is performed by a clutch motor connected with the engine to compensate the torque difference between the vehicle driving torque demand value and an engine torque by an assist motor.
The engine power is determined based on a value obtained by dividing the vehicle driving power by an efficiency of transmission of the engine power from the engine to the drive shaft of the vehicle to add a motor loss and an electricity storage device loss to the vehicle driving power demand value and the charge/discharge power demand value.
However, the engine performance characteristic changes and lessens because a fuel injection device is likely to clog and a cylinder bore and a ring are likely to wear during use. Further, the characteristic property of fuel serving as a material for generating the power energy of the internal combustion engine changes, depending on a season and a market. This also changes the performance of the engine. Furthermore, a similar problem occurs because the performance and characteristic of the power transmission device including the rotary electric machine and the electricity storage device change with age.
Thus, the most efficient engine operation point once determined as above is likely to deviate from an optimum one. Therefore, the vehicle driving power is dislocated from the vehicle driving power demand value or the electricity storage device is wastefully consumed.